The invention concerns treatment of vascular walls to prevent restenosis after balloon angioplasty and/or stent implantation, and particularly the invention concerns a catheter with an X-ray tube at its distal end, for performing such treatment.
As a treatment for coronary artery disease, balloon angioplasty, or percutaneous transluminal angioplasty has been used on an increasing basis. In a great number of cases, often estimated at up to 50 percent, restenosis occurs at the site where the angioplasty was administered. Restenosis is the re-closing of arteries after balloon angioplasty and/or stenting. The re-closing is caused by a hyperproliferative cellular response to the balloon and stent injuries. The scarring of the vessel can be sufficiently severe to obstruct blood flow through the vessel. As one type of countermeasure, stents have recently come into wide use, the stent being a metal, tubular vascular prosthesis which is implanted after angioplasty to mechanically hold the vessel lumen open. However, even with a stent in place, in-stent restenosis still tends to occur in more than 25 percent of cases.
Drugs have been suggested and tried for the purpose of preventing or limiting restenosis. These include heparin, dexamethasone and integralin, as well as others. These drugs have generally comprised anticoagulants and arterial smooth muscle proliferation inhibitors as well as agents to prevent aggregation of platelets. Catheters have been suggested for helping assure that the drug is applied directly to the site in question. Effective local application of such drugs is difficult and generally unproven as to effectiveness.
Radiation is known to be effective in reducing restenosis after angioplasty. This has been done using a radioactive isotope mounted on the tip of a catheter, emitting gamma or beta radiation, inserted into the vessel until the emitter is at the lesion location. Problems with the use of radioactive isotopes may include the need for a shielded operating room, with special care and handling of the radioactive sources and the catheter and problems of disposal; the effect of the radiation throughout the length of the blood vessel through which it is inserted, when only one particular site is desired to be irradiated; and inadequate control of the depth of penetration of the radiation from the isotope sources.
See, for example, U.S. Pat. No. 5,199,939 disclosing a catheter with a radioactive source for irradiating an angioplasty site to prevent restenosis.
U.S. Pat. Nos. 4,143,275, 5,153,900, 5,428,658, 5,422,926, 5,442,678, 5,452,720, 5,621,780, RE34,421, and PCT Publication WO 97/7740 all disclose X-ray devices for delivering radiation to remote positions in the body, including narrow passageways as small as blood vessels. Thus, these latter patents and publications describe radiation emitters which can be switched on and off, not involving use or handling of radioactive isotopes. Several of these patents describe probes with fiber optic cables leading to X-ray tubes, the fiber optic designed to carry light which activates a photo cathode in the tube. To date none of these proposed X-ray delivery devices has been built and effectively used in the human vascular system. Problems of X-ray absorption, sufficient power, lengthy treatment times, and bonding and sealing of the X-ray tube to the catheter have not been adequately addressed in the prior art.